1. Field of the Invention.
The present invention describes methods and apparatus for creating tissue necrosis. More specifically, this invention pertains to the creation of necrotic tissue having the effect of blocking conductive pathways. This invention may be used in the treatment of hypertension, cardiac, neurologic, renal, and various other disorders.
Hypertension affects an estimated one billion patients worldwide. The kidney is directly involved in body fluid homeostasis, and its ability to excrete sodium chloride and maintain sodium balance, extracellular fluid volume, and blood volume are major factors in the regulation of long-term arterial pressure. Both the kidneys and the autonomic nervous system contribute to kidney function, with the two being linked through the renal nerves.
The renal sympathetic nerves play a significant role in the pathophysiology of hypertension, where increased stimulation of these nerves triggers changes in renal vascular resistance, renin release, and retention of water and sodium. The afferent renal nerves monitor pressure changes in the kidney and relay the information to the central nervous system which then influences function of effector organs. Renal receptors influence cardiovascular function via increased activity of the sympathetic nerves to the kidney and other vascular beds and organs. The increase in sympathetic nerve activity and the activation of afferent renal nerves directly contributes to hypertension.
Untreated, hypertension can lead or contribute to cardiovascular (e.g. myocardial infarction, congestive heart failure), neurologic (e.g. stroke, dementia), and renal (e.g. chronic renal failure) disorders all having a direct effect on morbidity and mortality. Current therapies for hypertension primarily consist of lifestyle changes and pharmacological therapy, with varying degrees of success. In a subset of these patients with persistent hypertension, interventional therapy has been tested.
Initial treatment for hypertension is a change in lifestyle, including: diet, exercise, and weight loss, as well as elimination of smoking. Dietary modifications include limiting sodium intake, and consumption of nuts, whole grains, fish, poultry, fruits, and vegetables. In addition, a decrease in the consumption of red meats, sweets, and sugar is recommended. Exercise, weight loss, and non-smoking all contribute to improved cardiovascular function and decreased cardiac demand.
Pharmacologic approaches consist of individual or combinations of antihypertensive drugs, namely: diuretics, which reduce blood volume by eliminating sodium and water; beta blockers, which reduce cardiac workload and dilate blood vessels; angiotensin-converting enzyme inhibitors; Angiotensin II receptor blockers; and calcium channels blockers, all of which dilate blood vessels and may reduce heart rate; and renin inhibitors which decrease the production of renin, an enzyme in the chain that increases blood pressure. In addition to these medications, in certain cases these drugs are administered: alpha blockers, to reduce vasoconstrictive chemicals; alpha-beta blockers, which also reduce cardiac output; central nervous system agents to reduce vasoconstriction; and vasodilators, used to increase vessel diameter and reduce pressure. Combinations of all these medications are administered in light of their different effects on patients of varying race, gender, and age.
Patients taking multiple simultaneous medications without relief of hypertension are considered to have resistant hypertension. In the case of resistant hypertension, an invasive approach wherein the functionality of the renal nerves or sympathetic nervous elements is decreased or eliminated is proposed. This approach may also be applicable as a therapy for controlled hypertension.
While existing therapies may have demonstrated a limited effect in treating these disorders, improved systems and methods for creating necrotic tissue and effecting nerve activity are needed. Furthermore, it would be desirable for such systems to have an increased control in, for example: position, profile, and morphology of the generated necrotic tissue, while also offering greater patient safety and ultimately greater efficacy.
2. Background Art.
Other devices based on ultrasound energy to create lesions are described in U.S. Pat. Nos. 6,997,925; 6,966,908; 6,964,660; 6,954,977; 6,953,460; 6,652,515; 6,547,788; and 6,514,249 to Maguire et al.; U.S. Pat. Nos. 6,955,173; 6,052,576; 6,305,378; 6,164,283; and 6,012,457 to Lesh; U.S. Pat. Nos. 6,872,205; 6,416,511; 6,254,599; 6,245,064; and 6,024,740; to Lesh et al.; U.S. Pat. Nos. 6,383,151; 6,117,101; and WO 99/02096 to Diederich et al.; U.S. Pat. No. 6,635,054 to Fjield et al.; U.S. Pat. No. 6,780,183 to Jimenez et al.; U.S. Pat. No. 6,605,084 to Acker et al.; U.S. Pat. No. 5,295,484 to Marcus et al.; and WO 2005/117734 to Wong et al. Other related patents and patent publications include: U.S. Pat. Nos. 6,978,174; 7,162,303; 7,617,005; 7,620,451; 7,647,115; 7,653,438; 7,717,948; 7,756,583; 7,853,333; 7,873,417; 7,937,143; US20060212078; US20070173899; US20100137952; US20110060324; US20060212076; US20070265687; US20100168731; US20110112400; US20060265014; US20080213331; US20100168739; US20110166499; US20060265015; US20080255642; US20100174282; US20110178570; US20060271111; US20090036948; US20100191112; US20110200171; US20060276852; US20090062873; US20100222851; US20110202098; US20060025821; US20090076409; US20100222854; US20110208096; US20070129720; US20100137860; US20100249773; US20110257564; US20050234523; US20060041277; US20100268307; US20110264011; US20100010567; US20110264075.